Semiconductor circuit processing has seen dramatic improvements that allow semiconductor manufacturers to shrink the size of circuits formed on wafers. This shrinkage provides a cost advantage to the manufacturer because more circuits can be provided in a given area of a wafer surface. Semiconductor circuits generate a lot of heat caused by resistance to electricity running through the circuits. As density increases, the amount of heat generated also increases. Heat build up can impact the performance, reliability, and durability of electrical components. Thus, an efficient heat removal system is necessary.
Heat dissipating devices, such as heat spreaders, have been used to dissipate heat from electronic components. These devices draw heat away from the electronic components and spread it over a larger area for further heat removal. Surface contact between the heat dissipating devices and the electronic components is a factor in determining how efficiently the heat dissipating devices operate. Thermal conductivity between surfaces is related to the surface area that is in direct contact. Because surfaces of heat spreaders and electronic components are not perfectly flat or smooth, it is difficult to achieve perfect contact between surfaces. Because air is a poor thermal conductor, any air pockets between the surfaces can inhibit heat dissipation. To overcome this problem, thermal interface materials have been used to fill gaps between surfaces.
A variety of materials have been used as thermal interface materials, including phase change materials and metallic solder. The use of metallic solder can result in improved conductivity, but processes for their application to component surfaces have their drawbacks. Achieving a durable bond in the soldering process may involve reflow of the thermal interface materials. In addition, heating temperatures necessary to appropriately heat the solder may damage the electronic components.
Prior implementations of solder thermal interface materials (STIMs) used fluxless soldering in a vacuum oven in order to minimize voids in the STIM. One type of material that has been used in these fluxless soldering operations is Indium. Specialized equipment and knowledge was required in this process. Prior implementations also required the metallization of a silicon die at the die level. This required that the component manufacturer perform the operation. In addition, many prior implementations required STIM soldering prior to or coincident with mass assembly reflow. These prior methods often resulted in an impermanent bond between the STIM and the electronic component, which was undesirable. Fluxless bonding methods are known to have low throughput and involve high costs, which can make them unsuitable for high volume semiconductor manufacturing. Other prior implementations involved the use of flux, but the flux was known to cause voids, which resulted in reliability issues.